The invention relates to a data communication system based on a serial bus with a plurality of transmitter and/or receiver stations attached for intercommunicating multibit messages organized in physical frames that contain a sequence of a start signal, address signals and further signals, and also containing control signals, any said frame supporting an in-frame dialog in that it comprises both write information and read information as pertaining to art actual master station.
A single-channel bus has been described in U.S. Pat. No. 4,429,384 (PHN 9737), herein corporated by reference. Such a communication bus is particularly suited for transfer of control signals between various devices for consumer entertainment, devices for executing household chores, and devices for producing various maintenance and management control signals in a domestic environment. A different kind of serial bus has been disclosed in U.S. Pat. No. 4,689,740. This particular serial bus has separate clock and data wires. A still different set-up is a single data wire, a single clock wire, and a single word enable wire. A still different set-up is a single data wire, a single bit synchronization wire, and a single word synchronization wire. Serial in this context means that the information transmitted is represented by at most two wire signals, wherein in the case of two wires the information bit stream is represented by a logic combination between the signals on the two wires. Examples are an EXOR-function and a realization by a twisted or balanced wire pair, wherein the information is embodied by mutually opposite signals on the two wires. Apart from the one or two information-carrying wires, any other wire is exclusively used for controlling and/or synchronizing the transfer. For simplicity, only the system according to the first referenced patent is considered hereinafter. Now, a realistic system of course has at least one transmitter station and also at least one receiver station. Another discrimination is between master station and slave station. The master generally synchronizes the transfer in the context of the overall frame. Various different communication configurations such as one-to-one, one-to-many and others are common general knowledge. Now, the frame generally has a sequence of a start bit, mode bits indicating the intended transmission frequency, a master address, a slave address and data. Also, further control bits have been defined and allowance has been made for returning acknowledgement by the receiver, which in principle may be the master as well as the slave. A positive acknowledgement opens the way for a next transfer (such as a next byte). A negative acknowledgement may induce a repeat transmission. Inasmuch as on the bit level master and slave are only weakly interrelated, the particular outcome of the transfer may have appreciable effects on further synchronization. Now, other bus organizations have different standards for the start signals, the address signals, the control signals and the further signals, the latter of course also covering the data signals that would represent the information that the slave or destination station would really need. In certain situations, the transmitter may operate as master (i.e. synchronizer station) and the receiver as slave, but this is not a prerequisite, inasmuch as also the message may have the destination station as synchronizer. Also, a separate synchronizer station may be present.
A communication system is used with respect to stations that are manufactured by various different manufacturing entities. It has been found advisable to be able to test such stations for correct functioning by a monitor station. The station function so tested may be for correct interaction with the bus proper on a protocol level, or alternatively on the level of correct execution of an application program on a debug level. Furthermore, it may be the bus itself that is the subject of the test.